Assessment of in-service durability performance of natural draft cooling towers in a petrochemical environment

Abstract

Effective temperature control is an important operation requirement in petrochemical processes, where Cooling Towers (CT) play a key role in efficiently lowering water temperature for reuse in various chemical processes. Natural draft cooling towers function as heat extraction systems, dissipating thermal energy from hot water into the atmosphere through cold air. However, many reinforced concrete cooling towers have exhibited signs of deterioration over time, such as cracking, corrosion, and structural misalignment, posing the risk of structural failure. To address these issues, structural condition assessment programs, aiming to inspect, repair, and monitor cooling towers to prevent structural collapse are of significant importance. The focus of this study investigates the durability of natural draft cooling towers in an aggressive petrochemical environment. With a focus on Sasol Secunda Natural Draft Cooling Towers, the research aims to identify and characterize the various concrete deterioration mechanisms, quantify durability parameters, and explore mitigation measures for both new and existing cooling towers. Concrete deterioration is a significant concern in structures exposed to harsh environments, affecting their global stability and service life. The study examines the role of cover concrete quality in resisting corrosive agents and assesses durability using South Africa's three durability index (DI) tests, including water sorptivity, chloride conductivity, and oxygen permeability. The study comprised of on-site assessments and laboratory testing methods to determine the durability performance of cooling towers. The approach includes the three durability index tests. On-site assessments include visual inspections and non-destructive testing (NDT) near areas displaying signs of deterioration. The significance of this research relies on the operational efficiency of cooling towers in petrochemical plants, their vulnerability to harsh conditions, and the need for durability design considerations at Front End Loading (FEL) engineering and planning. It aims to shift from prescriptive to performance-based design approaches and provide insights for maintenance and mitigation strategies. This study contributes to the knowledge of concrete durability in challenging environments, aiming to enhance the longevity and performance of critical industrial infrastructure, particularly natural draft cooling towers.